Tools of the Trade: Look to the Moon

Recognizing weather signs at sea is something that even the middling sailor became familiar with relatively quickly in the ages of sail. Out in blue water, with nothing between you and disaster but wood, tar, rope, canvas and a hodge-podge of men, you would become acutely aware of your environment and its atmosphere. Knowing how to spot changes in weather before they became a problem was as critical to good sailing as dead reckoning and maintenance.


Since it would be dark, for the most part, twelve hours a day, relying on the sun and the clouds was only worth half your time. Given that fact, it probably comes as no surprise that the largest body in the night sky – the moon – was the first thing a sailor would look to at night for signs of weather to come.

Here, then, for your considerations are the basics of predicting weather by the moon courtesy of that much travelled navigator, privateer and sometimes pirate, William Dampier:

When the moon appears unusually large and bright, particularly if its tint is blue, count on bone-chilling winds.

The full moon in temperate latitudes – between the Tropics of Cancer and Capricorn – generally foretells fair weather for the three days she sails in the sky.

A pale moon, either purely white or mottled with gray, signals rain.

If the moon takes on a dirty, yellow cast, which Dampier refers to as “dull”, brutal heat and possible dead calms are in the offing.

A red moon, normally the domain of autumn by land but possible in any season at sea, foretells the return of high winds after calms or slow breezes.

Most interesting to me, perhaps because of the meticulous detail applied, is the forecasts possible when a hazy ring appears around the moon. This is a sure indication of stormy weather. If the atmosphere is already cool, look for sleet; if warm or hot, expect rain. Look more closely, though, and count the number of stars present in the ring. This information was thought to tell a sailor the number of days they had to prepare for the upcoming storm.

Thus the moon might save your life at sea, which is probably something moderns hardly think of. It was doubtless, however, a realization that rarely left the back of any historical sailors mind. At least if he knew what was good for him… or her.

Header: The Lovers Boat by Albert P. Ryder via Old Paint